North American Network Operators Group


Re: A transAtlantic cable was severed.

  • From: Gary R Wright
  • Date: Tue Feb 23 18:33:11 1999

At 04:24 PM 2/23/1999 -0500, Ravi Pina wrote:
> There's an obvious problem. How could they locate both ends,
> lift same, splice, and seal the cable in 24 hours?

If you are interested in how this is done, take a look at The article
is from December of 1996 and is a fascinating description of FLAG,
a 28,000 km fiber-optic cable between England and Japan.

Here is an excerpt regarding the repair ships:

	Clearly, submarine cable repair is a good business to be in. Cable
	repair ships are standing by in ports all over the world, on 24-hour
	call, waiting for a break to happen somewhere in their neighborhood.
	They are called agreement ships. Sometimes, when nothing else is
	going on, they will go out and pull up old abandoned cables. The
	stated reason for this is that the old cables present a hazard to
	other ships. However, if you do so much as raise an eyebrow at this
	explanation, any cable man will be happy to tell you the real
	reason:  whenever a fisherman snags his net on anything - a rock,
	a wreck, or even a figment of his imagination - he will go out and
	sue whatever company happens to have a cable in that general
	vicinity. The cable companies are waiting eagerly for the day when
	a fisherman goes into court claiming to have snagged his nets on
	a cable, only to be informed that the cable was pulled up by an
	agreement ship years before.

and here is a longer excerpt regarding the repair process:

	This raises two questions, one simple and one nauseatingly difficult
	and complex. First, how does one repair a cable if it's too tight
	to haul up?

	The answer is that it must first be pulled slightly off the seafloor
	by a detrenching grapnel, which is a device, meant to be towed
	behind a ship, that rolls across the bottom of the ocean on two
	fat tractor tires. Centered between those tires is a stout,
	wicked-looking, C-shaped hook, curving forward at the bottom like
	a stinger. It carves its way through the muck and eventually gets
	under the cable and lifts it up and holds it steady just above the
	seafloor. At this point its tow rope is released and buoyed off.

	The ship now deploys another towed device called a cutter, which,
	seen from above, is shaped like a manta ray. On the top and bottom
	surfaces it carries V-shaped blades. As the ship makes another pass
	over the detrenching grapnel, one of these blades catches the cable
	and severs it.

	It is now possible to get hold of the cut ends, using other grapnels.
	A cable repair ship carries many different kinds of grapnels and
	other hardware, and keeping track of them and their names (like
	"long prong Sam") is sort of like taking a course in exotic marine
	zoology. One of the ends is hauled up on board ship, and a new
	length of cable is spliced onto it solely to provide excess slack.
	Only now can both ends of the cable be brought aboard the ship at
	the same time and the final splice made.

	But now the cable has way too much slack. It can't just be dumped
	overboard, because it would form an untidy heap on the bottom,
	easily snagged. Worse, its precise location would not be known,
	which is suicide from a legal point of view. As long as a cable's
	position is precisely known and marked on charts, avoiding it is
	the responsibility of every mariner who comes that way. If it's
	out of place, any snags are the responsibility of the cable's

	So the loose loop of cable must be carefully lowered to the bottom
	on the end of a rope and arranged into a sideways bight that lies
	alongside the original route of the cable something like an oxbow
	lake beside a river channel. The geometry of this bight is carefully
	recorded with sidescan sonar so that the information can be forwarded
	to the people who update the world's nautical charts.

	One problem: now you have a rope between your ship's winch and the
	recently laid cable. It looks like an old-fashioned, hairy, organic
	jute rope, but it has a core of steel. It is a badass rope, extremely
	strong and heavy and expensive. You could cut it off and drop it,
	but this would waste money and leave a wild rope trailing across
	the seafloor, inviting more snags.

	So at this point you deploy your submersible remotely operated
	vehicle (ROV) on the end of an umbilical. It rolls across the seabed
	on its tank tracks, finds the rope, and cuts it with its terrifying
	hydraulic guillotine.